BIG is so negative because of so many bankruptcies and relatively few top-ranking players.
You lose points ("cumulative" score) for bankrupting as well as a host of other things that normally occur on the way to bankruptcy (strikes, fines, etc).
You each airline gets points ("variable" score) for being in the Top 20 of the following categories (if they have more than 10 planes): company image, total sales revenue (last quarter), punctuality, utilization, profit margin, and pax moved (past 30 days). Every airline in the Top 20 of each of those stats receives points (#1 gets 20 points, #2 gets 19 points, etc, etc, etc)
In theory a singular massive airline with superb efficiency and could theoretically earn 140 points all by themselves if they were #1 in every single category which would be virtually impossible. It also means that even being a couple airlines short of your competition can be a huge detriment.
The scoring methodology brings up some interesting results... like if you look at it, SkyNet and Silver Star the #2 and #3 positions are quite some distance away in points. But, in terms of airline performance we're virtually identical in score, SkyNet is just losing a lot of points due to a very large number if early bankruptcies. GlobalSky is in much the same basket, though I think their bankruptcies have been occurring along a more steady trend as the game has progressed.
Another interesting thing is that GlobalSky has almost the same number of "variable" points as both SkyNet and SilverStar, but they don't even have a single airline in the Top 10 of Pax (barely even Top 20 honestly) and only a small presence in Revenue, so they really have none of the "mega-airlines". They have a much more significant presence in things like punctuality and utilization, so they're earning points off different metrics that are "keeping them in the race" so to speak.
WorldSky is absolutely, utterly dominating in Europe where it's incredibly easy to maintain high utilization, high pax figures, and high profit margins, and did a superb job of locking in some of the biggest US bases as well (sans DFW
) earning them top-ranks in pax -- and as a result of that, and the fact they've done a remarkable job of having virtually no BKs, they are dominating the scoreboard.